Empty DC's apnList when the DC is free.
Not doing this causes DC.apnList's to have multiple entries in the
apnlist which causes DC's to look like its connected to both IMS and
INTERNET. And when selecting CDMA only mode on a Xoom we will not bring
up the connection thus no data connectivity.
Bug: 6939338
Change-Id: I17bc17cd1938ebac773db8131d12d0fa724348b0